Note 3 - Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Fair Value, Assets Measured on Recurring Basis [Table Text Block]

	As of December 31, 2017
	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets
Cash equivalents	$	11,662	$	-	$	-	$	11,662
Government securities		20,971		-		-		20,971
Total	$	32,633	$	-	$	-	$	32,633

	As of December 31, 2016
	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets
Cash equivalents	$	28,876	$	-	$	-	$	28,876
Government securities		4,925		-		-		4,925
Total	$	33,801	$	-	$	-	$	33,801

Available-for-sale Securities [Table Text Block]

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2017
Government securities
(Due within 1 year)	$	20,991	$	-	$	(20	)	$	20,971
	$	20,991	$	-	$	(20	)	$	20,971
December 31, 2016
Government securities
(Due within 1 year)	$	4,924	$	1	$	-		$	4,925
	$	4,924	$	1	$	-		$	4,925